1. Field of the Invention
This invention relates to a method and apparatus for producing a synthetic board from cellulosic and/or lignocellulosic materials utilizing a polyisocyanate binder system. The binder is applied to the hot and wet fibrous material in the blow line out of the refiner of the board forming process.
2. Description of the Prior Art
Many board products are manufactured by the basic process of consolidating or joining together bodies of cellulosic and/or ligno-cellulosic materials or furnish using pressure, heat and a chemical binder. Typical binders used in making such products are thermosetting resins such as phenol-formaldehyde, resorcinol-formaldehyde, melamine-formaldehyde, urea-formaldehyde, urea-furfural and condensed furfuryl alcohol resins. Another binder system, which has been gaining favor in recent years, involves the use of organic polyisocyanates, either alone or in combination with other binder materials, such as urea-or melamine-formaldehyde resins, phenol-formaldehyde resins, etc.
An advantage of polyisocyanate binders is that they can be used with high moisture-content furnish, thus reducing the costs of drying, and eliminating the "blue haze" sometimes found when drying to low moisture content. Also, the bonds developed with these binders are very resistant to water and thus have good exterior exposure characteristics.
Since polyisocyanate binders are highly reactive, their blending with the furnish is conventionally accomplished at low temperature and humidity conditions to avoid premature curing of the binder. Special blending equipment must be provided and maintained in good working order for this purpose. If the blending system is not properly constructed and operated, the result could be the production of inconsistent or low-quality board. It would be highly desirable if an improved method of producing a synthetic board from ligno-cellulosic and/or cellulosic materials and polyisocyanate binders could be found which yields a high quality board product without requiring any complicated or expensive blending equipment.